The present invention relates to the technical field of catalytic reaction or conversion of alcohols and aldehydes, in particular for the preparation of higher alcohols and/or aldehydes or mixtures thereof.
The present invention relates in particular to a process for preparing higher alcohols and/or aldehydes by catalytic reaction of ethanol.
The present invention further relates to the use of an activated carbon substrate provided with at least one metal as catalyst for the catalytic reaction of ethanol.
In addition, the present invention relates to a process for the chain extension of carbon compounds having oxo and/or hydroxy functions by catalytic reaction.
Finally, the present invention relates to the use of an activated carbon substrate provided with at least one metal as catalyst for the catalytic chain extension of carbon compounds having oxo and/or hydroxy functions.
Higher or relatively high molecular weight alcohols and aldehydes and mixtures thereof, in particular C3-C30-compounds (i.e. compounds having from 3 to 30 carbon atoms) of the abovementioned type have numerous uses in a variety of industrial fields and are therefore of great industrial importance: thus, higher alcohols and aldehydes are used in industrial processes, for example as solvents, as additives for plastics, paints and varnishes and also as fuels or fuel additives or else as starting materials or building blocks for further syntheses.
For the purposes of the present invention, the terms “higher alcohol” and “higher aldehyde” refer, in particular, to organic compounds having at least one hydroxy and/or aldehyde function and a carbon chain comprising at least three atoms, in particular C3-C30-compounds. The carbon chain can be linear or branched and can optionally be interrupted by ether functions.
Furthermore, the higher alcohols and/or aldehydes are generally compounds which are derived from aliphatic hydrocarbons, although part of the hydrogen atoms can be replaced, for example, by functional groups or heteroatoms, for example halogen atoms. However, it is also possible for the higher alcohols and/or aldehydes to be aromatic or partially aromatic systems having at least one hydroxy and/or aldehyde function.
C3-C10-alcohols or -aldehydes in particular are of great industrial importance: the primary alcohols of this type are used as solvents or for preparing plasticizers and surfactants and also as additives in varnishes and paints.
In addition, the compounds can also be utilized as starting materials or building blocks for further industrial processes. In this context, 1-butanol is of particular importance and represents a valuable C4 building block whose importance in the future will increase further due to the increasing spread of biosynthetic processes, known as “green processes”. Furthermore, 1-butanol can also be used for fuel production or as fuel. 1-Butanol can be added in considerable amounts to commercial spark-ignition fuels, with the use of 1-butanol having the advantage over the use of ethanol that butanol has a higher heating value but is essentially not hygroscopic. In addition, spark-ignition fuel having any proportion of 1-butanol and also pure 1-butanol can be burnt in the spark-ignition engines mass produced at present. For these reasons, the preparation of 1-butanol on the basis of renewable, usually biosynthetic processes is the subject of intensive research at present and 1-butanol from renewable processes is referred to as a third generation biofuel.
However, there have hitherto not been any available processes by means of which selective preparation of 1-butanol from ethanol can be carried out in an economically viable way on an industrial scale.
The corresponding aldehydes are employed as such or optionally after further reaction, in particular hydrogenation, for example as or in solvents, as fuels and fuel additives, as or in plasticizers or in varnishes and paints.
Relatively high molecular weight alcohols are nowadays produced mainly by the oxo process. In this process, propene produced from fossil sources is converted by means of synthesis gas and water into higher alcohols. The reaction requires a high pressure and additionally produces CO2. Increasing costs of fossil raw materials, the high energy consumption and the resulting greenhouse gas emissions make an alternative production method based on renewable raw materials desirable.
In particular, the preparation of higher alcohols and/or aldehydes from C1 and C2 building blocks, for example methanol and ethanol, would be particularly advantageous since these compounds are firstly often obtained as by-products or waste products in “green processes” and secondly can also be produced selectively and in a targeted manner from renewable raw materials.
Thus, for example, lignocellulose can be dissociated into sugars by thermal and/or chemical and subsequent enzymatic treatment and these sugars can be fermented by microorganisms to produce ethanol. In addition, the use of lignocellulose has the advantage that the woody constituents of plants which are not suitable for producing foodstuffs can be made available for further utilization. The utilization of lignocellulose consequently leads not to a competitive use of valuable food and animal feed plants for energy generation or for chemical synthesis; rather, the residues obtained in the growing of foodstuffs, in particular plant constituents which cannot be utilized, can be passed to further beneficial use.
There has therefore been no lack of attempts in the prior art to synthesize these compounds by means of various processes:
One possible way of preparing the higher alcohol butanol on the basis of renewable raw materials is the ABE synthesis. Here, a mixture of acetone, butanol and ethanol is produced by fermentation from biomass. A typical molar ratio of the constituents is 3/6/1. However, butanol is frequently obtained together with by-products of the synthesis and greatly diluted with water in this process. This mixture finally has to be purified with a high process outlay and water has to be separated off with consumption of a great deal of energy. Furthermore, large amounts of CO2 and of methane which is even more damaging to the climate are formed during the fermentation.
Apart from these two known processes, approaches using heterogeneous catalysis in order to produce higher alcohols from the alcohols ethanol or methanol are known. Thus, EP 1 829 851A1 discloses a catalyst based on hydroxyapatite, by means of which butanol, in particular, can be prepared at atmospheric pressure and temperatures up to 400° C. Disadvantages are, in particular, the low selectivity of the conversion into alcohols at relatively high temperatures and the occurrence of aromatic compounds and butadiene and also a low conversion at relatively low temperatures and a low space-time yield. A further disadvantage is the required high dilution of the starting materials or reactants with inert gas.
In addition, a series of further processes which, in particular, are disclosed in the international patent applications WO 2009/026518 A1, WO 2009/026483 A1, WO 2009/026501A1, WO 2009/026506 A1, WO 2009/026523 A1, WO 2009/097310 A1, WO 2009/026510 A1 and WO 2009/097312 A1 and in each case utilize hydrotalcite as catalyst in order to produce higher alcohols from ethanol and from ethanol/methanol mixtures are known. Disadvantages here are the relatively low conversion and the low space-time yield and the required high dilution of the reactants with inert gas, which stand in the way of an economical process.
The scientific publication by Olson et al. “Higher-Alcohols Biorefinery—Improvement of Catalyst for Ethanol Conversion”, 2004, Appl. Biochem. Biotechnol. Vol. 113-116, pages 913-932, describes a catalyst based on activated carbon, where activated carbons having BET surface areas in the range from 20 to 100 m2/g and impregnated with alkaline promoters are used as catalysts. However, these activated carbon catalysts are not stable in the synthesis of alcohols or aldehydes from ethanol or methanol and deactivate quickly. Owing to the short life of the catalysts, they cannot be used in industrial processes.
The abovementioned processes of the prior art all have the disadvantage that they produce higher alcohols or aldehydes in only small yields, in particular in low space-time yields, so that these processes are not very efficient and cannot be carried out economically feasibly. In addition, a difficult-to-achieve mode of operation with dilution of the starting materials or reactants with inert gas is necessary in the processes of the prior art. Most of the above-described processes of the prior art use catalyst systems having unsatisfactory operating lives of the catalysts under industrial conditions. It is also often difficult to create controllable reaction conditions so as to obtain reliably reproducible yields and product mixtures. Most of the processes are unsuitable for industrial applications.